This invention relates to cobalt compounds and methods of making cobalt powders. In particular, this invention relates to HCoO2 (heterogenite) and methods for making submicron cobalt powders.
Submicron particle size ( less than 1 xcexcm) cobalt powders exhibit distinct advantageous properties over larger, micron size ( greater than 1 xcexcm) powders. For example, in tungsten carbide applications, submicron size cobalt particles greatly improve sinterability and mass transport at temperatures significantly below the sintering temperatures required for micron-size cobalt powders. Typically, submicron cobalt metal powder is made via thermal decomposition of cobalt oxalate (CoC2O4). However, this method is not very efficient as CoC2O4 contains only 40 wt. % Co compared to 53.6 wt. % Co in Co(OH)3. Hence, it would be advantageous to use a compound having a higher cobalt content such as cobalt hydroxide to make submicron cobalt powders.
U.S. Pat. No. 4,218,240 teaches the conversion of Co(OH)3 to a micron-size cobalt metal powder having a FSSS value of 1.3-1.4 xcexcm. Impure CoCl2 in solution is converted to Co(NH3)6Cl3 which is then converted to Co(OH)3 by decomposition with NaOH. Cobalt powder is produced by direct reduction of the wet cobalt hydroxide in hydrogen at 300-500xc2x0 C. Although the patent describes air drying of the Co(OH)3 at 100xc2x0 C. to form a hydrated cobaltic oxide, it also teaches that air drying is not necessary prior to reducing the cobalt containing precipitate. No submicron powders are described.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a high-cobalt-content precursor material for making submicron cobalt metal powders.
In accordance with the objects of this invention, there is provided a heterogenite powder having a surface area of at least about 90 m2/g.